For fish, flow doesn't matter as much other than for oxygenation of the water or providing current for them to swim in. For corals, flow is much more important as it brings nutrients to them from the water column and helps get rid of their waste. Some corals require more flow than others but they all appreciate more random flow.
If your powerhead doesn't have a wavemaker function, you can set it on a timer to turn on and off at short intervals to create a wave action in the tank. Or you can have the powerhead run for a while at one speed, then turn it off for a short period, then back on. This will help create some random flow in the tank without having to buy a powerhead that has a wavemaker.